3D Mixed hex and tetra meshing

Dear sir/ Ma'am,

1) I have a 3D model for which I wish to do Hex meshing. I have divided my model in several parts and I could hex mesh some of them. But since I am       not able to hex mesh all of them I want to go with a mixed meshing i.e., tetra meshing for the remaining parts. May somebody please tell me the way       to achieve what I am wishing to do? [Please tell me the path to the suggested options in the hypermesh]

     I could have meshed my model completely with the 2nd order tetras but I want to have hex elements at the contacts.

2) Please, also tell me if there is any problem in using mixed (hex-pent- tetra) meshing in the transient (explicit) analysis. What type of elements (including for 2d meshing) are suggested for a transient structural analysis of a large assembly (also for the individual components) having loads applied for milliseconds? [It's not the case of crash analysis] 

Thank you in advance! /emoticons/default_smile.png' srcset='/emoticons/smile@2x.png 2x' title=':)' width='20' />